Solid-phase synthesis (otherwise known as “SPS”) is a well-established method that has revolutionised natural oligomer and small molecule synthesis and allowed for the development of combinatorial techniques and high-throughput drug discovery. Currently more and more articles are being published in the area (e.g. R. E. Dolle, J. Comb. Chem., 2000, 2, 383.; S. E. Hall, Mol. Diversity, 1999, 4, 131.).
The seminal work in this area is the famous Merrifield's peptide synthesis on crosslinked polystyrene (R. B. Merrifield, J. Am. Chem. Soc., 1963, 85, 2149.) even if the concept has been envisaged some years before (R. L. Letsinger and S. B. Hamilton, J. Am. Chem. Soc., 1959, 81, 3009.; R. L. Letsinger and M. J. Komet, J. Am. Chem. Soc., 1963, 85, 3045.).
The use of chemically inert, insoluble, crosslinked polymers to assist synthetic transformations has several advantages: most important, the system allows the use of excess reagents to drive reactions to completion which can be easily separated by means of a simple filtration and subsequent washings. For this reason, automation of a complete synthetic sequence in a single vessel has been possible accelerating the synthetic output even at industrial level.
As a consequence the development of improved polymeric supports is of paramount importance to solid-phase synthesis.
After Merrifield's peptide synthesis a wide variety of supports have been developed (e.g. I. Sucholeiki, Mol. Diversity, 1999, 4, 25; P. H. Toy, T. S. Reger, and K. D. Janda, Aldrichimica Acta, 2000, 33, 87; B. Yan, Comb. Chem. High Throughput Screening, 1998, 1, 215; D. Hudson, J. Comb. Chem., 1999, 1, 333; D. Hudson, J Comb. Chem., 1999, 1, 403; M. Meldal, Methods in Enzymology, 1997, 289, 83.). Polystyrene supports (cross-linked with divinylbenzene, usually <5%) are quite resistant (both chemically and mechanically) and can provide for high loading levels as each monomer may bear a functional group. Polystyrene polymers have been used as:                lowly-crosslinked gel-type resins (e.g. R. B. Merrifield, J. Am. Chem. Soc., 1963, 85, 2149.; R. L. Letsinger and M. J. Komet, J. Am. Chem. Soc., 1963, 85, 3045.; R. L. Letsinger and V. Mahadevan, J. Am. Chem. Soc., 1965, 87, 3526;. R. L. Letsinger, M. J. Komet, V. Mahadevan, and D. M. Jerina, J. Am. Chem. Soc., 1964, 86, 5163.; R. Arshady, Makromol. Chem., 1988, 189, 1295.; J. H. Adams, R. M. Cook, D. Hudson, V. Jammalamadaka, M. H. Lyttle, and M. F. Songster, J. Org. Chem., 1998, 63, 3706.),        macroporous supports (e.g. C. McCollum and A. Andrus, Tetrahedron Lett., 1991, 32, 4069; A. Mercier, H. Deleuze, and 0. Mondain-Monval, React. Funct. Polym., 2000, 46, 67; A. Barbetta, N. R. Cameron, and S. J. Cooper, Chem. Commun. (Cambridge), 2000, 221; Y. H. Chang and W. T. Ford, Journal of Organic Chemistry, 1981, 46, 5364; M. Hori, D. J. Gravert, P. Wentworth, Jr., and K. D. Janda, Bioorg. Med. Chem. Lett., 1998, 8, 2363.),        and even in a linear, soluble format (e.g. P. H. Toy and K. D. Janda, Acc. Chem. Res., 2000, 33, 546; D. J. Gravert and K. D. Janda, Chem. Rev., 1997, 97, 489).        
They have been used in different physical formats such as beads, monoliths (e.g. A. Mercier, H. Deleuze, and O. Mondain-Monval, React. Funct. Polym., 2000, 46, 67.) and discs (e.g. N. Hird, I. Hughes, D. Hunter, M. G. J. T. Morrison, D. C. Sherrington, and L. Stevenson, Tetrahedron, 1999, 55, 9575).
Nevertheless, solvent compatibility for polystyrene is low due to the hydrophobic nature of the polymer. This is particularly relevant for gel-type resins that need to swell well in the reaction solvent, or solvent mixture, to allow diffusion of reagents/substrates to the polymer bound substrates/reagents.
To improve these features several chemically different types of polymers were developed. Most successful alternatives for Merrifield resins being:                polyethylene glycol-(PEG)-containing polystyrene (PS) supports such as:                    Tentagel (e.g. E. Bayer and W. Rapp, U.S. Pat. No. 4,908,405.; A. W. Czamik, Biotechnol. Bioeng., 1998, 61, 77; Y. Feng and K. Burgess, Biotechnol. Bioeng., 2000, 71, 3; W. B. Li and B. Yan, J. Org. Chem., 1998, 63, 4092),            Argogel (e.g. J. W. Labadie, J. A. Porco and O. W. Gooding, WO 97 27226.; O. W. Gooding, S. Baudart, T. L. Deegan, K. Heisler, J. W. Labadie, W. S. Newcomb, J. A. Porco, and P. van Eikeren, J. Combi. Chem., 1999, 1, 113; A. W. Czarnik, Biotechnol. Bioeng, 1998, 61, 77; Y. Feng and K. Burgess, Biotechnol. Bioeng., 2000, 71, 3; Argonaut Technologies web-page: http://www.argotech.com),            Novagel (e.g. Y. Feng and K. Burgess, Biotechnol. Bioeng., 2000, 71, 3; Novabiochem web-page: http://www.novabiochem.com),                        non-divinyl benzene (DVB) crosslinked PS polymers such as:                    POEPS (e.g. M. Meldal, J. Buchardt and J. Rademann, WO 00 18823.; J. Buchardt and M. Meldal, Tetrahedron Lett., 1998, 39, 8695; M. Grotli, C. H. Gotfredsen, J. Rademann, J. Buchardt, A. J. Clark, J. O. Duus, and M. Meldal, J. Combi. Chem., 2000, 2, 108; M. Renil and M. Meldal, Tetrahedron Lett., 1996, 37, 6185);                        and JandaJel supports (e.g. P. H. Toy and K. D. Janda, Tetrahedron Lett., 1999, 40, 6329; P. H. Toy, T. S. Reger, and K. D. Janda, Aldrichimica Acta, 2000, 33, 87)        acrylamides polymers e.g. E. Atherton, D. L. J. Clive, and R. C. Sheppard, J. Am. Chem. Soc., 1975, 97, 6584.; R. Arshady, E. Atherton, D. L. J. Clive, and R. C. Sheppard, J. Chem. Soc., Perkin Trans. 1, 1981, 529; J. T. Sparrow, P. Kanda and R. C. Kennedy, U.S. Pat. No. 4,973,638) such as polydimethylacrylamide (PDMA) gels,        PEG-containing acrylamide supports, such as:                    PEGA resins (e.g. M. Meldal, U.S. Pat. No. 5,352,756.; M. Meldal, Tetrahedron Lett., 1992, 33, 3077; M. Meldal, F. -I. Auzanneau, O. Hindsgaul, and M. M. Palcic, J. Chem. Soc., Chem. Commun., 1994, 1849; M. Meldal and I. Svendsen, J. Chem. Soc., Perkin Trans. 1, 1995, 1591; M. Renil and M. Meldal, Tetrahedron Lett., 1995, 36, 4647)                        and all-PEG supports such as:                    SPOCC (e.g. M. Meldal, J. Buchardt and J. Rademann, WO 00 18823.; J. Rademann, M. Grotli, M. Meldal, and K. Bock, J. Am. Chem. Soc., 1999, 121, 5459; M. Grotli, J. Rademan, T. Groth, W. D. Lubell, L. P. Miranda, and M. Meldal, J. Comb. Chem., 2001, 3, 28; M. Grotli, C. H. Gotfredsen, J. Rademann, J. Buchardt, A. J. Clark, J. 0. Duus, and M. Meldal, J. Combi. Chem., 2000, 2, 108)            and POEPOP (e.g. M. Renil and M. Meldal, Tetrahedron Lett., 1996, 37, 6185; M. Grotli, C. H. Gotfredsen, J. Rademann, J. Buchardt, A. J. Clark, J. O. Duus, and M. Meldal, J. Combi. Chem., 2000, 2, 108; M. Grotli, J. Rademan, T. Groth, W. D. Lubell, L. P. Miranda, and M. Meldal, J. Comb. Chem., 2001, 3, 28).                        
Tentagel and related PEG-PS supports (Argogel and Novagel) are PEG-grafted PS polymers. The differences between these kinds of polymers lie in the structure of the graft bonds, the quantity of PEG chains per styrene monomer and the position of the functional site (at the end of the PEG chain or next to the aromatic ring). The amphiphilic towards hydrophilic and flexible nature of the PEG chains provides a good environment for reactions to take place and the PEG-grafted PS can swell well in both polar and non-polar solvents (from CH2Cl2 to water). As a disadvantage, the loading levels decrease dramatically from the PS supports, which for Merrifield resins can be up to 6.5 mmol/g resin, achieving at the most 1 mmol/g resin but normally much lower loading levels.
By grafting PEG chains the swelling behaviour of PS resins has been improved but at the cost of dramatically decreasing loading levels: a feature that has been repeated in support development.
Another way of improving the swelling properties of PS supports has been to use a crosslinker more flexible and hydrophilic than DVB. Two examples are POEPS resins and JandaJel. POEPS are PEG-crosslinked PS polymers. Their features are similar to PEG-grafted PS supports though, in theory, they allow for slightly higher loading levels.
JandaJel incorporates an oligomeric polytetrahydrofuran crosslinker which renders the resin more swellable in DMF and other polar aprotic solvents. Whilst this crosslinker allows the support to retain high loading levels it does not achieve a significant change in swelling properties since swelling is negligible in lower alcohols and water.
Alternatively, by changing completely the monomer to one that can present a functional polar side chain, capable of producing a polymer with excellent swelling properties and high loading levels, it was possible to produce a better support. For example, polyacrylamide resins possess good swelling in polar solvents and allow high loading levels constituting the best supports in solid-phase peptide synthesis (SPPS), especially for Fmoc chemistry. Nevertheless, their use is limited since amide bonds are chemically reactive in a wide variety of common organic reactions and therefore cannot be used for solid-phase organic synthesis (SPOS).
PEGA resins are acrylamide resins which include a PEG-containing crosslinker. Their features are similar to polyacrylamide resins.
So far, polyethers have proved the best option to produce supports with the chemical stability needed for SPOS applications and good swelling properties. This is the case of the “all PEG”-supports (such as SPOCC and POEPOP). They are constituted of functionalised crosslinked PEG. These polymers swell very well across a wide range of solvent polarities and are chemically resistant so that they can be used in SPOS. Nevertheless the loading levels achieved with these supports is low (typically far below 1 mmol/g resin) and their method of synthesis does not allow for a high control in functionality level or crosslinking level as it is carried out by the polymerisation of a non purified mixture of macromonomers and macrocrosslinkers.
The inspection of the features of available polymeric supports for synthetic applications shows that there is still the need for the development of a novel resin capable of fast swelling kinetics and high degrees of swelling in polar and apolar solvents, possessing chemical stability under a wide variety of reaction conditions to be compatible with SPPS, oligonucleotide synthesis and SPOS and with the possibility of high levels of control over the loading level. Ideally this support should also be able to be produced via the copolymerisation of different comonomers in a controlled and easy manner that would allow the presence of different functional groups in the desired ratio to be used for orthogonal processes.
Chemically stable off-the-shelf supports that interact well with a wide range of solvents have low loading levels (usually below 1 mmol/g) whereas supports with high loading levels are limited to a narrow range of suitable solvent systems (I. Sucholeiki, Mol. Diversity, 1999, 4, 25; P. H. Toy, T. S. Reger, and K. D. Janda, Aldrichimica Acta, 2000, 33, 87; B. Yan, Comb. Chem. High Throughput Screening, 1998, 1, 215; D. Hudson, J. Comb. Chem., 1999, 1, 333; D. Hudson, J. Comb. Chem., 1999, 1, 403; M. Meldal, Methods in Enzymology, 1997, 289, 83.). Support development has shown that polyether supports (usually but not necessarily PEG-derived) exhibit good swelling properties combined with good chemical stability. On the other hand, vinyl monomers can provide for side chain functional sites allowing high loading levels and high degree of control of these loading levels. In addition copolymerisation of different vinyl monomers allow the inclusion of a diverse range of functional sites in the final support. All of these characteristics are common to a unique type of monomers: vinyl ethers.
The present invention seeks to provide a support that posseses these characteristics and thereby overcomes the problems associated with the known polymeric supports.